Commercial “bag house” type filter installations typically consist of a plurality of parallel filter units, each containing a plurality of parallel rows of vertically arranged filter elements in the form of filter bags. Each such filter bag has a top end opening. A gas polluted with particulates is channeled through the filter bags to filter and collect particulates entrained in the gas. Hence, upon filtering and collecting the particulates entrained in the gas, a “cleaned gas” is produced. More specifically, cleaned gas is produced by channeling a polluted gas into a filter installation for passage through one or more filter units for gas flow from an exterior surface of a plurality of filter bags through to an interior area within the filter bags via flow through the sides of the filter bags. As the polluted gas passes from the exterior surface of the filter bags through to the interior area within the filter bags, particulate pollutants entrained in the gas are filtered and collected forming dust cakes on the exterior surfaces of the filter bags. Hence, gas in the interior area of the filter bags is the so produced cleaned gas. Cleaned gas exits the interior areas of the filter bags via a top end opening in each such filter bag. Cleaned gas flows from the top end openings through an outlet duct common to the filter units. During operation of the filter installation, a negative pressure is typically generated by a fan arranged downstream of the filter installation to cause gas flow through the filter units and filter bags.
As noted above, dust and particulates entrained in the polluted gas are filtered by and collected on the exterior surfaces of the filter bags, thus forming dust cakes thereon. Cleaning of the filter bags to remove the dust cakes is necessary for effective and efficient equipment performance. Cleaning of the filter bags is accomplished using a pressure medium in the form of compressed air pulses injected into the filter bags in a direction opposite to that of gas filtering. Rows of filter bags are cleaned successively using cleaning units arranged for each such given row. A cleaning unit cleans a row of filter bags by generating a compressed air pulse delivered substantially simultaneously to each filter bag in the given row. More specifically, each cleaning unit comprises a nozzle pipe arranged above and extending the length of the associated row of filter bags for cleaning. Each nozzle pipe includes a distribution pipe with a plurality of vertically downwardly projecting pipe sockets connected thereto. Each pipe socket is positioned straight above a filter bag top end opening within the associated row. The function of these pipe sockets is to direct via nozzles compressed air pulses into the respective filter bag top end openings. The pipe sockets usually have a diameter of about 1.5 to 2 times greater than the diameter of the nozzle associated therewith. The nozzles associated therewith consist of circular holes of varying diameter formed in the distribution pipe. The varying diameter of the circular holes along the distribution pipe is determined empirically based on the total number of pipe sockets/nozzles, requiring a uniform distribution of compressed air pulsed therethrough. As such, circular holes arranged in the distribution pipe a greater distance from the nozzle pipe are larger in diameter than those of circular holes arranged in the distribution pipe a lesser distance from the nozzle pipe. By so varying the diameter of the circular holes, a uniform distribution of compressed air pulsed therethrough is achieved.
In the cleaning of filter bags using a pulse of compressed air, a valve is temporarily opened to establish fluid flow between a compressed air tank and the nozzle pipe. Upon fluid flow between the compressed air tank and the nozzle, compressed air is pulsed through the nozzle pipe and its associated distribution pipe, pipe sockets and nozzles. As such, a compressed air pulse is supplied to each of the filter bags in the associated row of filter bags. Compressed air pulses supplied to the filter bags dislodge dust and particulates that collect and cake in and on the walls of the filter bags. Dust cakes formed on the filter bags are thereby loosened by the flow of compressed air from the interior areas of the filter bags, through the filter bag side walls, to an area in the filter unit exterior thereto. The resultant loosened dust cakes fall off the exterior of the filter bags for hopper collection.
In operating a cleaning unit, it is essential that the above-described pulse valve delivers a cleaning pulse of compressed air at a relatively high pressure with a relatively low consumption of compressed air. Pulse valves function by a cavity behind a plunge or membrane emptying through either a solenoid valve or a pilot valve, whereby the plunge or membrane is displaced by the differential pressure between the air tank pressure on one side of the plunge or membrane and the cavity pressure on the other side of the plunge or membrane. The plunge or membrane undergoes considerably acceleration and achieves considerable velocity upon displacement as a result of this pressure differential. Eventually the plunge or membrane impacts an end position with very high momentum. The plunge or membrane impacting the end position with very high momentum creates a significantly loud noise upon impact. Likewise, when the plunge or membrane impacts the end position, such impact creates relatively high mechanical stresses. Mechanical stresses on the valve shorten the operational life expectancy of the valve and add to the system's operation costs when performance is hampered and/or replacement is necessary. Further, the plunge or membrane typically bounces with several pressure peaks upon impacting the end position causing compressed air waste. Hence, to increase system performance and decrease system operational costs, a valve with decreased mechanical stresses, decreased operational noise, decreased compressed air waste and increased operational life expectancy is desired.